1. Field of the Invention
Present invention relates to a semiconductor device and method for manufacturing therefore. The present invention particularly relates to a semiconductor device which can be used for a thin semiconductor base board preferably such that it is possible to improve a production yield in a process for forming a bump by preventing a crack on the semiconductor base board caused by a stress in a process for forming the bump, and method for manufacturing therefore.
2. Description of Related Art
Conventionally, in a semiconductor device such as an IC (integrated circuit), an LSI (large scale integrated circuit), and a VLSI (very large scale integrated circuit), a bump is formed according to various methods. That is, in a method, a metal ball is compressed on a position such as a pad section for forming the bump on a silicon wafer (semiconductor base board). In other method, a bump is formed by printing a metal paste. Yet, in other method, a bump is formed by connecting a wire bonding. These methods are selectively determined according to factors such as a shape and size of bump to be formed.
Also, there are various shapes and sizes for the bump to be formed because various shapes and sizes are required for a final package.
Recently, further smaller and thinner semiconductor device has been required; thus, further thinner silicon wafer has been required inevitably.
Such a thin silicon wafer is produced by grinding one side of an oridinary silicon wafer.
FIGS. 5A to 5E show an example for manufacturing process for an ordinary thin silicon wafer. In these drawings, features such as a shape and a dimension ratio in a thin silicon wafer are described differently from actual dimensions.
In this manufacturing process, pads 2 which are made of an aluminum member are formed by performing a vapor deposition or a sputtering operation on predetermined positions on a surface 1a (other principal surface) of a silicon wafer as shown in FIG. 5A. A metal plating layer 3 which is made of a nickel member is formed on the pads 2 by a method such as a plating method. After that, a solder balls 4 are compressed on the metal plating layers 3, or a solder paste is applied on the metal plating layers 3.
After that, the solder balls 4 melts so as to be a solder layers 5 by heating the solder paste in a predetermined temperature as shown in FIG. 5B. Thus, bumps 6 in a two-layer-structure which are made of the metal layers 3 and the solder layers 5 are formed. Here, sometimes, a gold plating layer may be used instead of the solder layer.
Next, a wafer is tested for measuring an electric characteristics of the silicon wafer 1 in which the bumps 6 are formed.
Next, as shown in FIG. 5C, a protecting tape 8 is applied on the bumps 6, 6 . . . on the silicon wafer 1 via a bonding agent layer 7. Next, as shown in FIG. 5D, the silicon wafer 1 is mounted on a wafer stage 9 such that the protecting tape 8 contacts the wafer stage 9. A back surface 1b (a principal surface) of the silicon wafer 1 is ground by a predetermined depth by using a grinding device (not shown in the drawing). By doing this, a silicon wafer 12 which are formed by a predetermined depth can be obtained.
After the grinding operation, as shown in FIG. 5E, the protecting tape 8 is removed from the silicon wafer 12. The silicon wafer 12 as a final product is shipped after the necessary packaging is conducted.
FIGS. 6A to 6D show other example for a manufacturing process for an ordinary thin silicon wafer. In these drawings, features such as a shape and a dimension ratio in a thin silicon wafer are described differently from actual dimensions.
In this manufacturing process, as shown in FIG. 6A, pads 2 made of an aluminum member are formed in predetermined positions on a surface 1a on the silicon wafer 1 by performing a vapor deposition or a sputtering operation. A protecting tape 8 is applied on the surface 1a on which the pads 2 are formed. The silicon wafer 1 is mounted on a wafer stage 9 such that the protecting tape 8 contacts the wafer stage 9. A back surface 1b of the silicon wafer 1 is ground by a predetermined depth by using a grinding device (not shown in the drawing).
After the grinding operation, the protecting tape 8 is removed. As shown in FIG. 6B, a silicon wafer 12 having a predetermined thickness can be obtained by grinding the silicon wafer 1.
Next, as shown in FIG. 6C, metal plating layers 3 made of a nickel member or the like are formed on the pads 2 which are formed on the surface 1a on the silicon wafer 12 by a method such as a plating method. After that, solder balls 4 are compressed on the plating layers 3. Otherwise a solder pasta is applied.
After that, the solder balls 4 melt to form solder layers 5 by heating the solder paste in a predetermined temperature as shown in FIG. 6D. Thus, bumps 6 having a two-layer-structure which are made of metal plating layers 3 and the solder layers 5 are formed on the pads 2.
Next, the silicon wafer 12 is tested for measuring an electric characteristics of the silicon wafer 12 on which the bumps 6 are formed. The silicon wafer 12 as a final product is shipped after the necessary packaging is conducted.
However, in the above ordinary thin silicon wafer 12, there are various problems as follows.
For example, when the silicon wafer 1 is ground after the bumps 6 are formed, the back surface 1b of the silicon wafer 1 is ground under condition that a diamond grinding wheel 16 in which a diamond grains are embedded is rotated and compressed to the back surface 1b so as to grind the back surface 1b as shown in FIG. 7. In such a case, each bump 6 becomes a factor for compressing inside the silicon wafer 1; thus, a stress is applied inside the silicon wafer 1. As a result, protrusions 17, 17 . . . are formed in a corresponding position to bumps 6, 6 . . . on a back surface 1b of the silicon wafer 1 according to gaps made by the bumps 6. In such a case, there is a problem in that a flatness on a back surface 1b on the silicon wafer 1 cannot be realized.
In order to avoid such a decreased flatness, various methods are proposed. According to one of such methods, thickness of the protecting tape 8 is increased so as to soften the stress caused by each bump 6, 6 . . . . Alternatively, according to other method, a bonding agent which is pliable enough to absorb the gap caused by the bump 6 is used instead of the bonding agent 7 and the protecting tape 8. However, it is difficult to realize a complete flatness on a back surface 1b on the silicon wafer 1.
Also, when the bump 6 is formed after the back surface 1b on the silicon wafer 1 is ground, a lot of micro-cracks 18, 18, . . . exist by an approximately 1 μm of depth which are formed in a grinding operation on a back surface 12b on the thin silicon wafer 12 as shown in FIG. 8. Therefore, these micro-cracks 18, 18, . . . become a stress factor thereinside due to a compression 19 which is applied when the solder balls 4 are compressed; thus, there is a concern that a crack and a split occur on the silicon wafer 12. For such a case, it is common that the bump 6 is formed according to a plating method or a printing method instead of using the solder balls 4 such that too much stress is not applied on the silicon wafer 12. However, there are problems according to these methods because it is not possible to form a finer structure in the silicon wafer and the production cost is high.